Thin-film transistors (TFTs) are widely used as switching elements or drive elements in active-matrix display devices such as liquid-crystal display devices or organic electro-luminescence (EL) display devices.
There have been proposed techniques for adjusting the threshold value (that is, the threshold voltage) of TFTs in the method of fabricating TFTs to be used as switching elements or drive elements. For example, Patent Literature (PTL 1) discloses a technique for adjusting the threshold value of a TFT to an appropriate value, by doping a channel layer made from polycrystalline silicon with boron during TFT fabrication.